Modern society depends on the ready availability of energy. As the demand for energy increases, devices capable of efficiently storing energy become increasingly important. As a result, energy storage devices, including batteries, capacitors, electrochemical capacitors (ECs), hybrid ECs, and the like are used extensively in the electronics realm and beyond. In particular, capacitors are widely used for applications ranging from electrical circuitry and power delivery to voltage regulation and battery replacement.
Electrochemical capacitors (including pseudocapacitors and electric double-layer capacitors (EDLCs) (sometimes called ultracapacitors, among other names) are characterized by high energy storage capacity, rapid charge/discharge ability, and large cycle lifetimes, as well as other desirable characteristics including high power density, small size, and low weight, and have thus become promising candidates for use in several energy storage applications. One difference between electrochemical capacitors and batteries is that electrochemical capacitors can be charged and discharged quickly because they do not rely on chemical reactions to store energy, and they don't degrade significantly over their lifetime, even when charged and discharged rapidly. Electrochemical capacitors are also less sensitive to temperature than batteries. Hybrid ECs combine high power, fast charging capability, and long cycle life with higher voltages that increase the energy density over conventional EC capacitors. Hybrid ECs thus bridge the gap between traditional electrochemical capacitors and batteries in that they have higher power density than Li-ion batteries and higher energy density than EC capacitors. Also, hybrid capacitors can achieve efficiencies of 95% or more which is greater than the 70% efficiency exhibited by many batteries.
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the discussion of the described embodiments. Additionally, elements in the figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of the embodiments illustrated. Certain figures may be shown in an idealized fashion in order to aid understanding, such as when structures are shown having straight lines, sharp angles, and/or parallel planes or the like that under real-world conditions would likely be significantly less symmetric and orderly. The same reference numerals in different figures denote the same elements, while similar reference numerals may, but do not necessarily, denote similar elements.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation is thereby intended.